If he hasn't already moved on after your rejection, which most men would. Try to contact him and talk to him. I wouldn't get your hopes up to high though. You turned him down once and probably hurt him. He may not want anything to do with you now. Good luck with that!
I love a guy who had proposed to me some months ago but I rejected him. I still love him. What do I do?
Just tell him you love him and see what happens. Sometimes its that simple.